The invertebrate chordates have some vertebrate characteristics such as a dorsal tubular nervous system and notochord. Among such phyla lacking a vertebral column occurs the Hemichordata. The class Pterobranchia of this phylum has not previously been explored with respect to biologically active or other chemical constituents.
In late 1972, we collected by SCUBA (ca. 20 m) in the Indian Ocean Off Southeast Africa, in areas patrolled by the great white shark Carchorodon carchoris, specimens from this class of the marine worm (.about.5 mm long in tube colonies) Cephalodiscus gilchristi (order cephalodiscida). Two years later, methanol and water extracts of C. gilchristi demonstrated a confirmed active level against the U.S. National Cancer Institute's murine P388 lymphocytic leukemia (PS system) and obtained a 32-41% life extension at 25-37.5 mg/kg. Now after more than fifteen years of relentless research directed at discovering the active constituent(s) of C. gilchristi, we have succeeded in the isolation and structural elucidation of a series of powerful cell growth inhibitory substances with PS cell line ED.sub.50 of 10.sup.-7 to 10.sup.-9 .mu.g/ml. We have denominated these substances as "cephalostatin 1", "cephalostatin 2", "cephalostatin 3", and "cephalostatin 4".